This invention relates generally to gas turbine engines, and more particularly, to methods and apparatus for operating gas turbine engines.
At least some known gas turbine engines include, in serial flow arrangement, a fan assembly, a low pressure compressor, a high pressure compressor, a combustor, a high pressure turbine, and a low pressure turbine. The high pressure compressor, combustor and high pressure turbine are sometimes collectively referred to as the core engine. Known fan assemblies include a plurality of circumferentially-spaced apart fan blades that extend radially outwardly from a rotor or disk. Each fan blade includes an airfoil section and an integral dovetail root section. The dovetail section is received in a complimentarily configured dovetail slot formed in the rotor.
At least some known fan assemblies may be susceptible to damage resulting from the ingestion of foreign objects such as birds or hailstones into the fan. More specifically, when a foreign object impacts a fan blade, the fan blade, or a portion of the blade, may break off from the rotor disk potentially damaging adjacent fan blades or other engine assemblies or, if not contained by the fan casing, the aircraft itself.
To facilitate reducing an amount of blade material lost during an ingestion event, at least some known fan assemblies permit limited blade rotation within the dovetail slot when a sufficiently high force is exerted on the blade. Such limited blade rotation is beneficial in facilitating prevention of blade breakage. In other known fan assemblies, a fan platform extending between adjacent fan blades is fabricated with regions adjacent the fan blades that are frangible so as to preserve the rotation capability of the blades in impact situations. Furthermore, within at least some known assemblies, the fan platform may be fabricated from lightweight composite materials. Although such materials may provide better weight and fatigue advantages compared to metallic materials, the composite materials generally are more brittle than the metallic materials, and as such, may be more susceptible to damage from impact with foreign objects, especially at or near the frangible areas of the platform.